The present invention relates to an improved collar for a clutch, particularly a clutch used in selectively connecting and disconnecting a source of drive torque with a co-axial driven shaft. More particularly, the present invention relates to a collar wherein meshing surfaces of the torque source and the driven shaft are designed such that the collar is under a neutral axial force while under torque.
Various all-wheel-drive vehicles have been developed for higher stability and maneuverability during travel of the vehicles. Many such all-wheel-drive vehicles have a part-time four-wheel-drive feature, which can switch, as desired, between a two-wheel mode and a four-wheel mode. Four-wheel drive is highly desirable for off-road travel over rough terrain because of the greater reliability in traction in such conditions, but on the usual hard, improved surface roads, vehicles can be more economically operated as a two-wheel conventional drive vehicle. The capability of shifting of a four-wheel drive vehicle to two-wheel driving and return therefore is highly desirable dependent on the conditions of traction confronted.
All-wheel-drive vehicles of this type have a clutch on a rotatable drive shaft in order to selectively transmit drive torque from a power source via the rotatable drive shaft to the driven wheels. Many of these vehicles use a clutch mechanism which is selectively engaged and disengaged to switch the vehicle between two-wheel-drive and four-wheel-drive modes. The clutch typically employs a clutch collar and has meshing teeth for torque transmission from a drive shaft to an output shaft or gear. While these clutches generally provide reliable torque transmission, problems still exist in situations where the clutch must disengage under high torque loads or when the difference between the relative speeds of the shafts is large. These type of clutches have problems in that the meshing surfaces of the teeth are parallel to the input and output shafts, which requires a large operating force for disconnecting the shafts in order to overcome the meshing forces applied to the meshing surfaces, and also in that it produces a shock and noise due to impact engagement of the teeth when connecting the shafts if the difference between the rotational speeds of the shafts is too large.
Therefore, there exists a need for an improved manner of engaging and disengaging a clutch under heavy torque load without requiring a large operating force to engage or disengage the clutch collar.
It is an object of this invention to overcome the deficiencies in the prior art by providing an improved clutch shift collar mechanism wherein meshing surfaces of the torque source and the driven shaft are designed such that the collar is under a neutral axial force while under torque.
According to the present invention, a clutch collar, formed as a sleeve which is coaxial with a rotating shaft, is used to engage a clutch mechanism to transfer rotation to another member or the like. The shift collar is preferably splined to a rotating shaft and is slideable along the direction of the longitudinal axis of the shaft. In a first embodiment, the shift collar mechanism includes angled teeth adapted to engage similar angle teeth within one of the rotating shafts, wherein the angle teeth and splines are designed such that the shift collar has a neutral axial force under torque. Translation of the shift collar is preferably performed by means of a shift mechanism in association with a detent ball, used to lock the shift collar in place under torque load. When the shift mechanism and detent ball are moved to release the shift collar, the angle teeth and splines cause the shift collar to disengage, even under high torque load. In this manner the shift collar is self-unlocking.
In a second embodiment, the shift collar preferably engages another member via face teeth displaced from the centerline of a rotating shaft on which the collar slides. The face tooth angle is designed such that the force vector along the centerline of the rotating shaft due to torque is approximately equal to the friction force of the shift collar splines along the shaft centerline. A similar shift mechanism and detent ball to the first embodiment is used to move the shift collar into engagement with the shift collar being self-unlocking.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.